OpenGL terrain

Sometimes function : z:=f(x,y) has to be displayed in 3D for better viewability.
Here a solution in OpenGL is shown. It is suited for functions where f(x,y) is
a continous graph to be computed at any point within the intervall within
reasonable time. The component requests the function values at equidistant points.
It is not made to display randomly spaced values, or where the calculation takes
ages.

A rectangular area is defined in the constructor. After setting the x/y spacing
and supplying the function for the values, 'getvalues' gets the values. This is
required once, the values are stored. Calling 'display' builds the triangle strips.